The present invention relates to an adhesive composition to be used in production of a display unit, such as CRT (cathode ray tube) and LCD (liquid crystal display), integral with a touch panel by bonding the touch panel to the display unit. The present invention also relates to an adhesive film, a display unit integral with a touch panel made with the adhesive composition or adhesive film, and a process for producing them.
In recent years, there has been seen a general use of the display unit integral with a touch panel (which is integrally composed of a touch panel and a display unit such as CRT and LCD) for ATMs and CDs in banks, ticket vending machines in stations, and portable information terminals.
The display unit integral with a touch panel is, as shown in FIG. 2, composed of a touch panel 1, a display unit 2 (such as LCD), and a spacer 3 interposed between them. The touch panel 1 and the display unit 2 are separated from each other by a prescribed gap 4 (about 0.4 mm). Without this gap, the touch panel 1 under pressure by touching will come into direct contact with the display unit 2, thereby blurring the images. This problem is likely to arise in the case of LCD display unit, because the layer of liquid crystal easily distorts to give blurred images.
Unfortunately, the gap between the touch panel and the display unit reflects, scatters, and absorbs light, thereby decreasing the contrast of display, an important factor as a display, by half. This lowers visibility and causes parallax and shade at the time of input.
Therefore, it is desirable to eliminate the gap by bonding the touch panel directly to the display unit. Unfortunately, there has been no adhesive available for this purpose. An adhesive such as epoxy resin adhesive is not suitable because it forms a hard adhesive layer which transmits pressure directly to the display unit when the touch panel is pressed. This results in blurred images. Moreover, an epoxy resin adhesive is poor in wetting properties and hence does not give a uniform adhesive layer.